1. Field of the Invention
The present invention generally relates to subsurface disposal techniques and, more particularly, is concerned with a downhole stuffing box assembly and pump barrel manifold seal coupling.
2. Description of the Prior Art
Over the past few years methods have been introduced that could allow the production of gas from a productive formation and, simultaneously, the disposal of drainage, such as water, from the productive formation in the same well bore. These methods would virtually eliminate the cost of disposal of co-produced water that is ordinarily pumped to the surface and transported to another disposal well.
To achieve simultaneous disposal of the gas production drainage water, the well must have a lower non-productive water-bearing disposal formation that will accept the drainage water. A pressure greater than the water injection pressure of the disposal formation is required to force the drainage water into the disposal formation. An isolation packer is required between the well tubing and casing to isolate the upper productive formation from the lower non-productive disposal formation.
Currently, there are three types of methods being used to force drainage water into the disposal formation with varying degrees of success. A first type is a gravity method as disclosed in U.S. Pat. No. 5,176,216 to Slater et al. This patent discloses a sucker rod actuated reciprocating insert pump and a by-pass seating nipple at the base of the production tubing string above the isolation packer. The seating nipple has a central passage receiving the pump and is closed at its lower end. The seating nipple has side intake ports communicating with the central passage and the pump and a series of longitudinal by-pass holes drilled through the length of the nipple side wall and circumferentially spaced from the side intake ports. Gas rises in the casing annulus as drainage water separates via the influence of gravity and flows downward in the casing annulus to the side intake ports of the seating nipple. The drainage water is then pumped upwardly through the tubing string in a conventional manner by the insert pump until the static weight of the water column equals the water injection pressure of the disposal formation. Continued upward pumping of additional drainage water causes drainage water from the water column to migrate downward via the influence of gravity through the longitudinal by-pass holes in the seating nipple to below its closed lower end and therefrom to the disposal formation.
In the event that the water injection pressure of the disposal formation is fairly low, the height of the water column in the tubing string may be fairly low. The rod string connected to the pump will then be stroking dry throughout its length from the top of the water column to the well surface. This would cause extreme friction and rod and tubing wear. Furthermore, there would be less downstroke plunger force and the rods could go from neutral to compression as opposed to from tension to compression. This condition has caused rod box connections to loosen and unscrew. On the other hand, in the event the water injection pressure is greater than the total weight of the water column, pressure will be created at the surface polish rod seal. High surface pressure could cause premature packing wear and leakage. When measurable surface pressure is maintained along with low annulus fluid volume or the well is pumped off partially, a high gas-to-water ratio is being pumped. This will create gas pockets in the tubing string and at the surface and cause excessive surface seal packing wear. Severe gas locking may occur in the pump, causing pump damage and poor pump performance.
A second type is a disposal formation injection method as disclosed in U.S. Pat. No. 5,425,416 to Hammeke et al. This patent discloses a downhole or below production disposal (BPD) injection tool connected to a modified insert or tubing pump that has a rod lift supported solid plunger with traveling seals (no traveling valves) that pumps down rather than up. The BPD tool has one-way ball and seat type valves built internally around the outer radius and a back pressure valve (check valve) inside the tool discharge passage at the base. On the upstroke drainage water from the productive formation is drawn into the pump cylinder via the one-way valves, and on the downstroke is discharged downward out through the back pressure valve, through the production isolation packer and into the disposal formation. The tubing above the plunger is loaded full with static water. The weight of the tubing water assists the rod string weight in providing the forces needed for the plunger downstroke to inject the drainage water into the pressurized disposal formation.
The BPD injection method has had problems maintaining a full static tubing load, causing the rod string to “stack out” on the downstroke. Also, if the tubing ID and the sucker rods are not thoroughly clean when the system is installed, trash (scale, etc.) will settle out on top of the plunger. A close fit tolerance of the barrel plunger is required, to prevent fluid slippage. The use of lip type traveling plunger seals soon wear from static tubing fluid trash and extreme friction heat when gassy fluid is pumped. There are other factors that also contribute to accelerated plunger seal wear. A considerable amount of tension must be maintained on the isolation packer to provide the isolation seal and to eliminate tubing movement from the stroking action of the pump. Most well bores are somewhat deviated. As the isolation packer is run below the pump and set in tension, the pump barrel is pulled out of alignment against the tight side of the casing. No top plunger wear bearing or tubing or barrel centralizer is used in this method.
A third type is the progressive cavity pump method which has had problems controlling low pumping rates when the annulus fluid is pumped off. When rate volume cannot be controlled and the fluid is pumped off, rapid heat build up occurs causing premature pump failure. Also, the use of submersible pumps is quite expensive and may be cost prohibitive in some wells.